The invention relates to a method of forming a silicon nitride film and a method of manufacturing a semiconductor device, and more particularly, to a method of forming a silicon nitride film having good step coverage by the catalytic CVD method and a method of manufacturing a semiconductor device.
Silicon nitride film plays an important role in various applications such as passivation film, etching stopper, and hard mask in semiconductor devices. Furthermore, it is used as gate sidewall for forming LDD (lightly doped drain) structure of MOSFET (metal-oxide-semiconductor field effect transistor).
Conventionally, silicon nitride film used for these applications is formed by the plasma CVD (chemical vapor deposition) method or photo-CVD method (see, e.g., Japanese Laid-Open Patent Applications 2002-75992 and S61-234534 (1986)).
However, use of the plasma CVD method involves some problems such as plasma charge-up of the wafer, leaving room for improvement in recent ultrafine semiconductor devices as typified by the 65-nm node generation. On the other hand, use of the photo-CVD method does not involve damage by charged particles. However, it has a low deposition rate because of low decomposition rate of raw material gas, and hence there is a problem that it is not suitable to mass production.
In this respect, the catalytic CVD method is recently developed. In the catalytic CVD method, raw material gas is contacted in a reduced pressure atmosphere with a metal filament heated, for example, above 1600° C., and thus subjected to decomposition and/or activation by catalysis to deposit a thin film on a substrate. The catalytic CVD method avoids damage caused by using plasma, and does not require radio-frequency power supply. It can thus significantly simplify the configuration of the apparatus.
Furthermore, in the conventional plasma CVD method, the usage efficiency of raw material gas is only a few percent. On the contrary, in the catalytic CVD method, a usage efficiency of nearly 80 percent can be achieved. In addition, it has a high deposition rate, and can deposit a thin film of high quality that is low in hydrogen content.
However, the inventor has found upon investigation that coverage for steps and grooves have room for improvement in a silicon nitride film formed by the catalytic CVD method. More specifically, when a silicon nitride film is deposited by the catalytic CVD method using silane (SiH4) and ammonia (NH3) as raw material, the deposition rate is low on the side surface of steps on the substrate and inside the grooves. If the pressure during deposition is decreased and the feed rate for ammonia relative to silane is decreased, the coverage is improved, but a silicon-rich thin film is formed because of insufficient nitridation of silicon.